Slide attenuator



Filed June 1, 1965 5 Sheets-$heet l FIG.

/lVl/E/VTOR CHESTER F. SCOTT Aug 22 1967 c. F. scoTT SLIDE ATTENUATORFiled June l, 1965 5 Sheets-Sheet 5 M-Hllv I /NI/E/VTOR CHESTER F. SCOTT,Lf/7*" By/qqb? AAW AGE/VT United States Patent O 3,337,831 SLIDEATTENUATOR Chester F. Scott, West Caldwell, NJ., assignor to Mc-Graw-Edison Company, Elgin, Ill., a corporation of Delaware Filed .lune1, 1965, Ser. No. 460,444 Claims. (Cl. 2538-126) ABSTRACT 0F THEDISCLOSURE The invention relates to a variable attenuator of a laddertype housed in a rectangular case having a central slot-like spacerunning therethrough from top to bottom. The attenuator is in twosections comprising two printed circuit boards in a spaced relationshipforming sidewalls of the slot-like space through the case. The circuitboards have slide contacts and resistor elements only on theiroppositely facing surfaces confronting the sidewalls of the case. Aswitch control member which bridges the circuit boards at the top haswipers which eng-age the slide contacts and a central handle whichextends outwardly of the case through the central slot. Each printedside of the circuit boards comprise 'a .series of transverse barsmounted side-by-side having upper end portions in a row constitutingswitch contact terminals and lower apertured portions to receive the endwires or resistors connected between the bars. Also, the printed side ofeach circuit board has a slip bar lengthwise thereof along the row ofslide contact terminals along which the respective switch wiper ismovable by the handle to connect it selectively to the switch Icontactterminals. Some of the transverse bars have an extended length to enableeasy connection of parallel resistors of the attenuator to a commonground bar at the lower end of the circuit board.

This invention relates to `a novel construction of a slide attenuatorwherein the contact means are protected from dust and dirt which mayfall on the attenuator when it is mounted on a horizontal panel.

The invention relates especially to a so-called ladder form ofattenuator comprising a series of pi-type resistor networks with meansfor making input connections selectively at taps along the series armsof the networks.

Further, the invention relates to such attenuators which have arectilinearly movable switch armature. However, no unnecessarylimitation of the invention to this specic form of attenuator hereindisclosed is intended.

In communication systems the attenuators are often mounted on horizontalpanels with the result that dust and dirt, especially cigarette yashes,may fall on and collect on o'r in the attenuator. If such dirt ispermitted to reach the switch contacts it will ultimately cause abreakdown in the proper functioning of the attenuator.

An object of the invention is to provide a novel attenuator having athrough space from top to bottom through which falling dirt may passwithout reaching the switch contacts of the attenuator.

Another object is to provide an attenuator of a novel and durableconstruction which is highly dependable in operation and economical toproduce.

Other objects and features of the invention will be apparent from thefollowing description and the appended claims.

In the description of my invention, reference is had to the accompanyingdrawings of which:

FIGURE 1 is an isometric View of the present slide attenuator.

FIGURE 2 is an isometric view similar to FIGURE 1 but with the casemostly broken away to show the in- 3,331,83 l Patented Aug. 22, 1967 iceternal construction, and wherein only part of the resistors forming theattenuator are shown so as not to becloud the circuit arrangement on theprinted circuit boar-ds;

i FIGURE 3 is a diagrammatic layout of the printed boards iand of theresistors connected thereto forming the two attenuator sections, thelower of the two sections being the rear section in FIGURE 2 .shownaligned with the front section but in an inverted position relativethereto; and

FIGURE 4 is a fractional schematic circuit diagram of the presentattenuator.

The present slide attenuator shown in the accompanying drawings ishoused in a rectangular case 10` comprising two rectangular side covers11a and 11b secured by screws 12 to a central rectangular frame 13formed by bending a relatively heavy met-al strap into a U-shape havinga flat top wall 13a with depending end walls 13b and 13e and footportions 13d and 13e bent inwardly from the respective end walls. In thetop wall 13a there is a central slot 14 running lengthwise thereof.Secured by screws 15 to the inner sides of the end walls yare verticalbars 16a and 1Gb. Secured to the opposite sides of these bars by screws17 are rectangular printed circuit boards 18 and 19. These boards haveprinted circuit bars on their outer sides confronting the sidewalls 11aand 11b of which the bar arrangement on the rear board 19 is a virtualimage of the arrangement appearing on the front board in FIGURE 2.

In describing the printed circuit boards 18 and 19 the components on therear board 19 corresponding to those on the front board 18 in FIGURE 2are given the same reference characters increased by as appearsparticularly in the diagrammatic showing in FIGURE 3. A description ofthe printed board 18 will therefore suiice as a description for bothboards.

The printed board 18 has a slip bar 20 near the top extending lengthwiseof the case throughout the length of the slot 14. Below the slip bar isa series of `seperate elongate transverse contact bars 21 having upwardterminal portions 21a in a row along and directly below the slip bar.The contact bars have terminal wire holes 22 directly below the terminalportions 21a and have also terminal wire holes 23 in their lower or farend portions. Connected between successive contact bars 21 are seriesresistors 24 each having one terminal wire in `a hole 22 of one contactbar and the other terminal wire in a hole 23 of the next succeedingcontactV bar. In order that these series resistors may stand verticallywithin the case the body portions of the transverse Contact bars areobliquely disposed so that the holes 23 and 24 of successive contactbars are vertically arranged.

Certain selected ones of the contact bars 21 have depending terminals21c each provided also with a terminal wire hole 25. In the illustrativeexample herein shown, the first contact bar and every fourth contact barthereafter through seven intervals, are so provided with the dependingterminals 21C. These depending terminals serve as connector tabs for aset of parallel resistors 26 the other ends of which are received interminal wire holes 27 in a common connector bar 28 located below andextending along the row of connector bars 21. Thus, a series of pi-typeresistance networks is formed on each printed board. The networks onboth printed boards have a common ground connection forming a laddertype attenuator as shown in FIGURE 4.

Located between the `printed circuit boards is a `rod 29 extendinglengthwise of the case and supported at its ends in holes 30 provided inthe end walls 13b and 13e. Mounted on this rod is a slide 31. Also, onend portions of the rod are rubber grommets 32 serving as bumpers forthe slide. The slide is manually movable by a finger piece 33 extendingupwardly through the slot 14. The slide has a pair of L-shaped sidelingers 34a and 34b extending across and downwardly alongside the topportion of the printed board 18 and has a similar pair of L-shaped sidefingers 134a and 13417 extending across and downwardly alongside the topportion of the board 19. Secured by screws 35 to the fingers 34a and 34bis a plate 36 of insulating material to a central portion of which isriveted a bridging contact 37 having one depending contact finger 37aslidably engaging the slip bar 20 and another depending contact finger37b slidably engageable with the terminal portions 21a of the contactbars 21. As the slide is moved by the finger piece 33 the slip bar isconnected selectively to the terminal portions 21a to make selectiveconnection to the junctions between the series resistors 24.

At the back side of the attenuator as it appears in FIG- URE 2 the slidehas a bridging contact 137 engaging the printed board 19 in the samemanner as the bridging contact 37 engages the printed board 18. Thus,selective connections are made in an identical manner to the twosymmetrical attenuators on the printed boards 18 and 19.

Further, as is shown in FIGURE 4, input circuit connections 38 are madeto the slip bars 20 and 120 and output circuit connections 39 are madeto the rst contact bars 21 and 121 at the left or start position of theslide. Also, a ground connection 40 is made to the common connector bars28 and 128. When the slide is at its start position a direct connectionis made from the slip bars to the output leads, but resistors 41 areserially connected to the slip bars so that there will be an initialinsertion loss of several db.

The attenuator may for example have 37 steps designed to provide aninsertion loss of 1.5 db per step throughout the 28 steps runningthrough the seven pi networks and to provide a db loss per stepthroughout the remaining portion of the attenuator according to thedesired taper for mixing controls which is 2, 3, 4, 4, 4, 4, 7, and oifTo this end the iirst parallel resistors 26 and 126 (at the left end ofthe attenua-tor as shown in FIGURE 4) may have 903 ohms, the subsequentparallel resistors of the seven identical pi sections may have 451.5ohms; the series resistors 24 and 124 in each of the seven identical pisections may have values proceeding from left to right of 60 ohms, 60ohms, 57 ohms and 49 ohms; and the'series resistors following the sevenidentical pi sections may have in sequence from left to right 82 ohms,

111 ohms, 106 ohms, 62.5 ohms, 35.2 ohms, 21 ohms,

17.75 ohms, 9.85 ohms and 4 ohms respectively. At their far or rightends the 4 ohm resistors are connected by leads 42 to the groundconnector bar 28. All lead connections (input, output and ground) to andfrom the attenuators are made via a connector plug 43 in a foot portion13d of the frame as shown in FIGURE 2.

As is apparent from the foregoing description the present attenuator hasa through slot from top to bottom from which the nger piece 33 projectsfor adjusting the slide. This slot is determined within the case bysidewalls which are constituted by the inoperative sides of the printedcircuit boards 18 and 19. All operative components of the attenuatorsare in the side spaces between the printed boards and the sidewallswherein they are fully shielded from dirt by the walls of the case andthe printed boards. Also, any dirt which may fall into the slot can passout through the bottom without accumulation in the case and withoutinterfering with the operation of the attenuator. This design makes heattenuator especially suitable for mounting on horizontal panels.

The embodiment of my invention herein particularly shown and describedis intended to be illustrative and not necessarily limitative of myinvention since the same is subject to changes and modications withoutdeparture 'from the scope of my invention, which I endeavor to expressacording to lthe following claims.

I claim:

1. A slide attenuator comprising two rectangular printed circuit boardsmounted in spaced parallel relationship, each of said printed circuitboards having on its outer side a series of transverse elongate contactbars mounted side-by-side with terminal portions in a row lengthwise ofthe board and with resistor-wire holes in lrows also lengthwise of theprinted board of which a rst row of holes is intermediate of the lengthsof the contact bars at the inner ends of said terminal portions and asecond row of holes is at the far ends of the contact bars opposite saidterminal portions, each of said printed circuit boards having also aslip bar lengthwise of the board and adjacent said row of terminalportions, series electrical resistors connected between successivecontact bars with one terminal wire of each resistor engaging anintermediate hole in a respective contact bar and the other terminalwire of the resistor engaging a far end hole of a next adjacent contactbar, a supporting rectangular frame for said printed circuit boardssurrounding said boards edgewise thereof, a rod between said printedcircuit boards supported at its ends by the end walls of said frame, aslide mounted on said rod having side portions extending beyond theouter sides of said printed circuit boards, a top wall of said framehaving a -slot of a width less than the width of the space between saidprinted circuit boards and of a length equal approximately to the`length of said slip bar, a handle on said slide extending outwardlythrough said slot, and a bridging contact mounted insulatedly on eachside portion of said slide beyond the edge of said slot for connectingthe respective slip bar to said terminal portions selectively as saidslide is moved manually along the printed boards.

2. The slide connector set forth in claim 1 wherein selected ones ofsaid contact bars separated by predetermined numbers of interveningcontact bars are provided with extending connector tabs at their farends, including parallel resistors connected between said selected barsand a common ground, and including input circuits connected to said slipbars whereby each printed board is connected as a series of pi-typeresistor networks having a plurality of taps along the series arm ofeach network selectively connectable to the respective input circuit bysaid slides.

3. The slide connector set forth in claim 2 including a connector barextending lengthwise of each printed board adjacent said Afar ends ofsaid contact bars, said extending terminal portions and said connectorbar being provided with terminal wire holes receiving the terminal wiresof said parallel resistors, and a lead wire connection to said connectorbar lfor connecting the connector bar to ground.

4. A slide :attenuator comprising a rectangular protective case having anarrow width dimension relative to its length and height dimensions, twospaced printed circuit boards mounted in said box in spaced parallelrelation to each other and in spaced parallel relation to the side wallsof the case, each of said printed circuit boards having a series ofseparateV contact bars spaced in va row lengthwise of the box and havinga continuous slip bar at one side of said row and a continuous groundconnector bar at the other side of said row extending throughout thelength of said row, said bars of each printed circuit board being on theouter side of the printed board confronting the respective side wall ofsaid case, series resistors connected between successive contact bars,parallel resistors connected between selected contact bars and saidconnector bar, said resistors being located in the spaces between saidprinted boards and said side walls of 4the case, the top wall of saidcase having a slot midway between said printed boards and extendinglengthwise of the case throughout the length of said row of contactbars, said printed boards being oiset' from the sides of said slot inthe side spaces of said case and said case having a bottom opening toprovide a through space between the printed circuit boards via said slotfor dirt falling onto the box, a slide between said printed boardsmounted for movement lengthwise thereof, a handle on said slideextending outwardly through said slot, and contact bridging lmembers onopposite sides of said slide each having one terminal slidably engagingsaid slip bar and another terminal selectively engageable with saidcontact bars as said slide is moved by said handle.

5. The slide lattenuator set forth in claim 4 wherein the contact bararrangement on one of said printed circuit boards is a virtual image ofthe other whereby to provide two symmetrical pi-type resistor networkswith a common ground along which identical connections are tions betweenthe respective series resistors as said slide is moved.

References Cited UNITED STATES PATENTS 2,617,911 11/1952 Carey etal.338-126 X 2,903,633 9/1959 Cother 338-188 X 3,307,133 2/1967 Wolff338-188 X FOREIGN PATENTS 15,970 10/ 1928 Australia.

RICHARD M. WOOD, Primary Examiner.

made selectively by said slide from said slip bars to junc- 15 J. G-SMITH, Assistant Examiner.

1. A SLIDE ATTENUATOR COMPRISING TWO RECTANGULAR PRINTED CIRCUIT BOARDSMOUNTED IN SPACED PARALLEL RELATIONSHIP, EACH OF SAID PRINTED CIRCUITBOARDS HAVING ON ITS OUTER SIDE A SERIES OF TRANSVERSE ELONGATE CONTACTBARS MOUNTED SIDE-BY-SIDE WITH TERMINAL PORTIONS IN A ROW LENGTHWISE OFTHE BOARD AND WITH RESISTOR-WIRE HOLES IN ROWS ALSO LENGTHWISE OF THEPRINTED BOARD OF WHICH A FIRST ROW OF HOLES IN INTERMEDIATE OF THELENGTHS OF THE CONTACT BARS AT THE INNER ENDS OF SAID TERMINAL PORTIONSAND A SECOND ROW OF HOLES IS AT THE FAR ENDS OF THE CONTACT BARSOPPOSITE SAID TERMINAL PORTIONS, EACH OF SAID PRINTED CIRCUIT BOARDSHAVING ALSO A SLIP BAR LENGTHWISE OF THE BOARD AND ADJACENT SAID ROW OFTERMINAL PORTIONS, SERIES ELECTRICAL RESISTORS CONNECTED BETWEENSUCCESSIVE CONTACT BARS WITH ONE TERMINAL WIRE OF EACH RESISTOR ENGAGINGAN INTERMEDIATE HOLE IN A RESPECTIVE CONTACT BAR AND THE OTHER TERMINALWIRE OF THE RESISTOR ENGAGING A FAR END HOLE OF A NEXT ADJACENT CONTACTBAR, A SUPPORTING RECTANGULAR FRAME FOR SAID PRINTED CIRCUIT BOARDSSURROUNDING SAID BOARDS EDGEWISE THEREOF, A ROD BETWEEN SAID PRINTEDCIRCUIT BOARDS SUPPORTED AT ITS END BY THE END WALLS OF SAID FRAME, ASLIDE MOUNTED ON SAID ROD HAVING SIDE PORTIONS EXTENDING BEYOND THEOUTER SIDES OF SAID PRINTED CIRCUIT BOARDS, A TOP WALL OF SAID FRAMEHAVING A SLOT OF A WIDTH LESS THAN THE WIDTH OF THE SPACE BETWEEN SAIDPRINTED CIRCUIT BOARDS AND OF A LENGTH EQUAL APPROXIMATELY TO THE LENGTHOF SAID SLIP BAR, A HANDLE ON SAID SLIDE EXTENDING OUTWARDLY THROUGHSAID SLOT, AND A BRIDGING CONTACT MOUNTED INSULATEDLY ON EACH SIDEPORTION OF SAID SLIDE BEYOND THE EDGE OF SAID SLOT FOR CONNECTING THERESPECTIVE SLIP BAR TO SAID TERMINAL PORTIONS SELECTIVELY AS SAID SLIDEIS MOVED MANUALLY ALONG THE PRINTED BOARDS.